This invention relates to hub clutch assemblies mounted on the front wheels of a four-wheel drive vehicle for selective transmission and cutoff of the driving force between the axle and the wheel hubs.
A part-time four-wheel drive vehicle is provided with a hub clutch assembly between the front wheel axle and each front wheel hub for selective transmission and cutoff of the driving force to and from the front wheels.
FIGS. 3 and 4 show a conventional hub clutch assembly that uses air pressure for such selective transmission and cutoff of driving force. It comprises a spindle 2 mounted around a front wheel axle 1 of a four-wheel drive vehicle and fixedly supported to a knuckle of the vehicle, and a wheel hub 4 rotatably supported by the spindle 2 through a bearing 3.
A cover 5 is secured to the end of the wheel hub 4 by bolts 6 with a gasket 7 interposed therebetween to seal the end of the wheel hub 4. The hub clutch assembly further includes an inner ring 8 as a driving member mounted on the axle 1 near its end by serrations 9 so as to be axially movable but non-rotatable relative to the axle 1. The inner ring 8 is formed on its outer periphery with an external gear 10.
The hub clutch assembly further includes an outer ring 11 as a driven member mounted to the inner surface of the cover 5 through serrations 12 so as to rotate together with the cover 5. On its inner periphery, the outer ring 11 carries an internal gear 13 so as to mesh with the external gear 10 on the inner ring 8.
Inside the cover 5, a diaphragm 14 has an outer edge airtightly secured to the inner periphery of the cover 5, and an inner edge airtightly secured to the inner ring 8 so as to be movable together with the inner ring 8. The outer edge is sandwiched between sleeve 27 and a yoke (not numbered). The diaphragm 14 thus defines two airtightly sealed chambers 15 and 16 at both sides thereof inside the cover 5. By supplying air into one of the chambers 15, 16 and sucking air from the other, it is possible to axially move the inner ring 8 to bring its external gear 10 into or out of mesh with the internal gear 13 of the outer ring 11. Four-wheel and two-wheel drive modes thus change over.
The inner ring 8 is biased inwardly by a spring 17 mounted in a compressed state between the diaphragm 14 and the cover 5. A magnet 19 (FIG. 4) is centrally fixed to the inner surface of the cover 5 through a yoke 20. Opposite the magnet 19, the diaphragm 14 carries on its outer side a magnetizable plate or washer 18. When the inner ring 8 is at its outermost position, the magnet 19 attracts the plate 18, thus holding the inner ring at this position.
For changeover between four-wheel drive and two-wheel drive modes, the hub clutch assembly has two separate air passages 21 and 22 communicating with the chambers 15 and 16, respectively.
The first air passage 21 comprises a passage 21a formed in the cover 5 and communicating with the chamber 15, a space 21b between the spindle 2 and the wheel hub 4, a gap inside the bearing 3 communicating with the space 21b, and a passage 21c formed in the rear end of the spindle 2 and communicating with the gap in the bearing 3. The passage 21c is connected to an air source through an air pipe 23.
The second air passage 22 comprises a gap 22a between the front wheel axle 1 and the spindle 2 and communicating with the inner chamber 16, and a passage 22b formed in the rear end of the spindle 2 and communicating with the gap 22a. The passage 22b is connected to an air source through an air pipe 24.
The chambers 15 and 16 are airtightly sealed by an oil seal 26 disposed between the inner surface of the cover 5 and a nut 25 threaded onto the tip of the spindle 2.
To set the drive mode into a four-wheel drive position, the inner ring 8 is moved until its external gear 10 meshes with the internal gear 13 of the outer ring 11.
In this state, the front wheel axle 1 is coupled to the outer ring 11 for four-wheel drive, so that the engine drive can be applied to all four vehicle wheels.
For changeover from four-wheel drive to two-wheel drive, the air in the outer chamber 15 is sucked therefrom to let the inner ring 8 move against the force of the spring 17 by the pressure difference on both sides of the diaphragm 14 until the external gear 10 disengages from the internal gear 13 (FIG. 3). The inner ring 8 is held in this position by the magnet 19.
Changeover between four-wheel drive and two-wheel drive is carried out by creating negative or positive pressure in the chamber 15 or 16. The two-wheel drive position is maintained by the attracting force of the magnet 19. The four-wheel drive position is maintained by the force of the spring 17.
The diaphragms of such conventional hub clutch assemblies all have a hardness of 71 Hw or greater for durability, and are arranged such that no stresses act thereon with the inner ring disengaged from the outer ring.
Although a diaphragm having a hardness of 71 Hw or greater is durable enough, a large thrust is needed to deform such a diaphragm for changeover from two-wheel drive to four-wheel drive.
Especially if the diaphragm is arranged such that no stresses act thereon when the inner ring is disengaged from the outer ring for a two-wheel drive mode, when pressure is applied for changeover to four-wheel drive, the fluid pressure is first used to deform the diaphragm, so that the thrust by the fluid decreases accordingly. This may make the changeover to four-wheel drive difficult. This is because for changeover to four-wheel drive, the external gear 10 has to be brought into mesh with the internal gear 13 by moving the inner ring 8, and a greater thrust is needed to mesh the gears with each other than to disengage them from each other.
An object of this invention is to provide a hub clutch assembly which can be changed over to four-wheel drive mode with a reduced thrust.